1. Field of the Invention
The present invention relates to a method of fabricating a titanium nitride layer, and more particularly, to a method of fabricating a titanium nitride layer to reduce thermal budget of the fabrication process as well as to remove hydro-carbon impurities within the titanium nitride layer.
2. Description of the Prior Art
In modern semiconductor processes, metal organic chemical vapor deposition (MOCVD) is gradually replacing the traditional sputtering process. The MOCVD uses metal organic compounds to form a thin metal film, such as tungsten (W), aluminum (Al), tantalum nitride (TaN) or titanium nitride (TiN), or a ferroelectric film, such as BaSrTaOx (BST), on a semiconductor substrate. However, using MOCVD also brings some disadvantages. For example, hydro-carbon impurities are also formed within the titanium nitride layer during the deposition process of the titanium nitride layer. As a result, the resistance of the titanium nitride layer is increased.
Please refer to FIG. 1 and FIG. 2. FIG. 1 and FIG. 2 are schematic diagrams of a method of fabricating a titanium nitride layer on a semiconductor wafer 10 according to the prior art. As shown in FIG. 1, the semiconductor wafer 10 comprises a silicon substrate 12, a bottom conducting layer 16 positioned on the silicon substrate 12, a dielectric layer 18 with a low dielectric constant (low K) positioned on the bottom conducting layer 16 as an inter-metal dielectric (IMD) layer, and a plurality of plug holes 20 positioned within the dielectric layer 18 (only a plug hole 20 is shown in FIG. 1). Therein, the bottom conducting layer 16 is an aluminum wire, and an anti-reflection coating (ARC) 17 of titanium nitride (TiN) is formed on the aluminum wire. As for the plug hole 20, it is used to form a tungsten plug therein in a later process, so as to electrically connect to the bottom conducting layer 16. The bottom conducting layer 16 functions as a gate, a source or a drain of a MOS transistor.
Following that, as shown in FIG. 2, a MOCVD is performed to deposit a titanium nitride layer 26 on the side wall of the plug hole 20, the titanium nitride layer 26 functioning as a barrier layer. The reaction of the MOCVD can be illustrated in the following reaction equation:
Ti[N(CH3)2]4xe2x86x92TiN(C,H)+HN(CH3)2+hydro-carbon impurities
As shown in the equation, after the deposition of the titanium nitride layer 26, some hydro-carbon impurities are also formed within the titanium nitride layer 26 by the MOCVD. As a result of the occurrence of the hydro-carbon impurities, the resistance of the titanium nitride layer 26 is increased and the uniformity of the products is affected.
In order to solve the above-mentioned problems, after the MOCVD is completed, a plasma treatment is required to remove the hydro-carbon impurities within the titanium nitride layer 26 and simultaneously densify the titanium nitride layer 26. However, the plasma treatment encounters some problems. During the plasma treatment, the silicon substrate 12 is often heated to above 420xc2x0 C. and aluminum within the bottom conducting layer 16 may extrude to the surface of the titanium nitride layer 26 to affect the tungsten plug""s RC value. In addition, under such a high temperature, the structure of the dielectric layer (low K IMD layer) 18 is damaged.
It is therefore a primary objective of the present invention to provide a method of fabricating a titanium nitride layer to reduce thermal budget and remove hydro-carbon impurities within the titanium nitride layer.
It is another objective of the present invention to solve the problem of aluminum extrusion.
It is still another objective of the present invention to prevent damage on the low K IMD layer.
According to the claimed invention, a MOCVD is used to form a titanium nitride layer on the surface of a semiconductor substrate. After that, a pulsed plasma treatment is performed to remove hydro-carbon impurities from the titanium nitride layer. Therein, the pulsed plasma treatment is performed in a pressure chamber. The pressure chamber comprises nitrogen gas (N2), hydrogen gas (H2) or argon gas (Ar). The pressure of the pressure chamber is controlled at between 1 and 3 Torr, and the power of the pressure chamber is controlled at between 500 and 1000 watts. In addition, a chiller is used to control temperatures cooling off the backside of the semiconductor substrate, so as to ensure the multi-step plasma treatment is performed with the temperature of the semiconductor substrate less than 390xc2x0 C.
It is an advantage of the present invention that the temperature of the semiconductor substrate is prevented from going too high, so the characteristics of the semiconductor elements are not destroyed. In addition, the thermal budget of the fabrication process is reduced and the hydro-carbon impurities are effectively removed according to the present invention.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, that is illustrated in the various figures and drawings.